1. Field of the Invention
The present invention relates generally to chemical mechanical polishing (CMP) fabrication techniques, and more particularly to the use of a polishing stop layer to achieve CMP thickness variation control, with particular application to the fabrication of magnetic heads.
2. Description of the Prior Art
Various types of thin film devices, such as magnetic heads for hard disk drives, are fabricated in large quantities on a single substrate surface. Following fabrication the substrate is sliced, or diced to provide a large quantity of discrete devices for later incorporation into various component assemblies. In the thin film fabrication process various features of the devices are fabricated utilizing precise thin film deposition and/or removal techniques, and it is often necessary that the thin film layers be deposited on a flat surface. To achieve such a flat surface during a fabrication process, a chemical mechanical polishing (CMP) process step is typically undertaken. Such a typical CMP step involves the use of a wet slurry that is disposed on a large, flat, moving polishing surface or table. Slurry chemistries can be quite complicated, and generally include a water base with additives to provide a basic or acidic pH depending upon the chemistry of the thin films formed on the substrate, together with an abrasive material. Substrate surfaces to be polished are placed upon the slurry coated flat polishing table and the movement of the table and slurry acts to polish the substrate surface.
To achieve a good product yield from a substrate, it is desirable to have good process control of the CMP step. Problems exist in the prior art CMP process control in that it is often the case that the polishing rate varies across the surface of the substrate, typically polishing is greater towards the edges of the substrate than at the center. Additionally, variations in the chemical composition and/or physical distribution of the slurry across the polishing table surface can result in uneven polishing of the substrate. It is also important to control the polishing depth, that is, the thickness of material that is removed from the substrate surface. Because material removal rates can vary across the substrate, polishing substrates for a particular time period can result in unequal CMP material removal from different substrate areas. It is therefore desirable to have a means for determining when the CMP polishing step has proceeded to a predetermined depth and to achieve uniform polishing across a substrate surface.
The present invention solves these CMP processing problems by the inclusion of a thin film polishing stop layer in the substrate fabrication process. With such a layer it then becomes possible to achieve a more even substrate polishing across the surface of the substrate, as well as to determine when the CMP polishing step has removed the appropriate thickness of material from the substrate.
The method for controlling the depth of polishing during a CMP process involves the deposition of a polishing stop layer at an appropriate point in the device fabrication process. The stop layer is comprised of a substance that is substantially more resistant to polishing with a particular polishing slurry that is utilized in the CMP process than a polishable material layer. Preferred stop layer materials of the present invention are tantalum and diamond-like-carbon (DLC), and the polishable layer may consist of alumina. In one embodiment of the present invention the stop layer is deposited directly onto the top surface of components to be protected during the CMP process. A polishable layer is thereafter deposited upon the stop layer, and the CMP polishing step removes the polishable material layer down to the portions of the stop layer that are deposited upon the top surfaces of the components. The stop layer is thereafter removed from the top surface of the components. In this embodiment, the fabricated height of the components is preserved.
In another embodiment of the present invention a first material layer is deposited following the fabrication of upwardly projecting components upon the substrate surface. A polishing stop layer is thereafter deposited upon the first material layer, and a polishable layer is then deposited upon the stop layer. In a subsequent CMP polishing step the substrate surface is polished down to height of the stop layer that is deposited upon the first material layer. Thereafter, the stop layer is removed. In this embodiment the height of the components is determined by the thickness of the first material layer. In the embodiments of the present invention the CMP end point is determinable by monitoring the electrical current of the polishing motor that is utilized in the CMP process.
In the CMP polishing method described above, the xe2x80x9ccomponentsxe2x80x9d can be magnetic pole pieces or induction coil turns of a magnetic head, or other components of recording heads, semiconductor devices or micro electrical mechanical systems (MEMS).
It is an advantage of the method for determining a CMP polishing end point of the present invention that uniform polishing of components across the surface of a substrate is obtained.
It is another advantage of the method for determining a CMP polishing end point of the present invention that a more uniform height for upwardly projecting components can be obtained during a CMP polishing process.
It is a further advantage of the method for determining a CMP polishing end point of the present invention that a CMP polishing end point can be more easily determined.
It is yet another advantage of the method for determining a CMP polishing end point of the present invention that component parts of magnetic heads that undergo a CMP process step can be more reliably fabricated.
It is yet a further advantage of the method for determining a CMP polishing end point of the present invention that the product yield of a plurality of components that are fabricated on a substrate which undergoes a CMP process step can be increased.
These and other features and advantages of the present invention will become well understood by those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawings.